Include hardcoded value for BTC transfers

For [getBridgedToken](https://github.com/Near-One/bridge-sdk-js/blob/da9e097efee4eefb5390f72fa6bd2d7480aaafb5/src/utils/tokens.ts#L72) function from SDK we could include the hardcoded value of nbtc.bridge.near -> BTC transfers